This invention relates to apparatus for controlling the thickness of a sheet extruded by a sheeting die and more particularly to die adjustment mechanism for mechanically adjusting the position of any selected one of a plurality of die bolts which adjust the position of a die lip and the size of a die opening.
Sheets of plastic, such as that formed from styrene resins, have been previously extruded via a sheeting die including a die body having an elongate opening therein. The die body includes generally parallel, coextensive extruding lips defining the elongate die opening or slot through which the plastic is extruded to form the sheet. One of the lips is integrally, flexibly connected to the remainder of the die body via a relatively thin web and can be adjustably positioned to control the size of the die opening and thereby control the thickness of the sheet being extruded. A plurality of die lip adjusting bolts are longitudinally spaced along the die body and bear against longitudinally spaced portions of the lip. The rotary positions of the bolts can be controlled by rotating the bolts about their axes to control the positions of longitudinally spaced portions of the lip.
In one sheeting die, the temperature of an exposed portion of each bolt is controlled by an individual heater which changes the length of the bolt as required to change the lip opening. As the bolt expands and contracts, it adjusts the position of a flexible die lip and controls the thickness of the plastic sheet extruded via the sheeting die. The heated bolt concept requires not only a control signal to change the dimension of the bolt but also requires continued maintenance of a given signal to maintain the adjustment. Such a system is relatively sophisticated and difficult to maintain.
Accordingly, it is an object of the present invention to provide new and improved apparatus for controlling the thickness of a sheet continuously derived from a machine.
It is another object of the present invention to provide an adjustment mechanism for a sheeting die of the type described which will mechanically adjust the positions of the die bolts.
It is yet another object of the present invention to provide a mechanical die adjusting mechanism of the type described which will respond to a signal to rotate the bolts and change the position of the die bolts and which will maintain the bolts in the adjusted positions without a continuous control signal from the control system.
It is a further object of the present invention to provide die bolt adjusting mechanism including a carriage which moves in a to-and-fro path of travel and includes mechanism for selectively adjusting any one of a plurality of rotatable die bolts.
A still further object of the present invention is to provide die bolt adjusting mechanism including a reciprocable carriage mounting a plurality of die bolt actuating members movable between a removed position and a position engaging selected one of said bolts and mechanism for selectively operating any selected one of the actuable means to selectively adjust the position of any bolt.
A further object of the present invention is to provide apparatus for mounting the die adjusting mechanism on a sheeting die while permitting expansion of the die relative to the adjusting mechanism.
Other objects and advantages of the present invention will become apparent to those of ordinary skill in the art as the description thereof proceeds.